Institutional Repository of GuangZhou Institute of Energy Conversion, CAS
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Increasing cerium dispersion favours lattice oxygen activity of cobalt oxides for CO catalytic combustion
No full textRemoving carbon monoxide with catalytic combustion technology is an effective and economical solution. Highly efficient conversion of CO at low temperatures can be achieved by introducing a catalyst, and its application in automotive exhaust emissions and preferential oxidation of CO in fuel cells is remarkable. In this work, catalysts were prepared by mixing the prepared cerium organic framework with Co3O4, and after calcination at 400 degrees C, the organic framework collapsed, resulting in a uniform dispersion of Ce on the Co3O4 nano surface. Experimental results demonstrated that the required temperature of the catalyst is 101 degrees C when the conversion is 90 %, and it remained stable over the 75 h tested at 100 degrees C. High resolution transmission electron microscopy (HRTEM) revealed that Ce/Co3O4 primarily exposed 311 surface. Combined with DFT calculations, the catalysts may improve the catalytic combustion activity of CO by multiplying the oxygen vacancies and modulating the dispersion of Ce atoms. The reaction occurred on the 311 surface predominantly. Activated CO* preferred to react with the lattice oxygen at the Ce-O-Co linkage compared to the lattice oxygen at Co-O-Co. Energy barrier for the rate dictating step in the complete catalytic cycle is 0.42 eV. This work not only provides experimental support and theoretical basis for the design of low-temperature catalytic combustion CO catalysts, but also provides new ideas for the doping of metal oxides with lanthanide metals
A model-based study of the evolution of gravel layer permeability under the synergistic blockage effect of sand particle transport and secondary hydrate formation
No full textWhen using gravel-packed completions to exploit hydrates, the synergistic blockage of gravel filling layer by sand and hydrate often arises. In this paper, we completed two kinds of permeability measurement experiments: experiments with different volume proportions of sand particles and experiments with different hydrate saturations in the pores of gravel filling layer. The variation in the permeability of a gravel filling layer under the simultaneous blockage due to small sand particles invasion and hydrate formation was studied experimentally. Based on the different assembly forms of spherical particles and classic permeability theory models, this paper first established an experimental model of the permeability of gravel filling layer formed by the secondary formation of hydrates under different sand volume proportions. Second, this paper analyzed the permeability measurement data. A modified permeability model based on the synergistic blockage mechanism of sand and hydrate in the gravel filling layer was obtained. Finally, this study revealed the permeability evolution of the gravel filling layer under sand intrusion and hydrate formation. The experimental data and permeability theory model results supported the following con-clusions: (1) The assumption of sand particles gathering in clusters in the pores has a similar impact on permeability as the formation of hydrates at the center of the pores, resulting in an exponential decrease in permeability as the proportion of sand particles increases. (2) Based on the changes in the surface areas of pores in a gravel filling layer during the processes of sand intrusion and hydrate growth, a theoretical model of the relative permeability of gravel filling layer was established. (3) Analyzing the permeability measurement experimental data revealed that the presence of small sand particles in the experiment was more conducive to the formation of hydrates, and a high saturation of hydrates may have formed in some areas, leading to more serious blockages in the gravel filling layer. This study validated the effectiveness of the theoretical model of relative permeability through permeability measurement experiments and explored the mechanism of cooperative sand and hydrate plugging, providing a theoretical basis for the safe and efficient exploitation of hydrate reservoirs
Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development[E239kf0401]
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Experimental studies on the OH* chemiluminescence and structure characteristics in NH3/H2 and NH3/cracked gas swirl flames
No full textAmmonia (NH3) has been gaining popularity as a carbon-free alternative fuel in recent years. OH* chemiluminescence is a promising method to study the structure of ammonia flames, but research on this aspect is still lacking. In this study, the OH* chem-iluminescence distributions and structure characteristics in NH3/H2 and NH3/cracked gas swirl flames are experimentally investigated. The OH* distributions of NH3/H2 and NH3/ cracked gas under different addition levels and equivalence ratios are compared. The re-sults show that the increase of equivalence ratio and hydrogen doping level significantly increased the OH* chemiluminescence peak of NH3/air swirling flame. Especially in fuel-lean flames, the equivalence ratio effect is greater than the NH3 dilution effect, while the two effects are comparable in equivalence and fuel-rich conditions. The stretching effect of NH3/cracked gas is stronger, and the flame width is narrower than that of NH3/H2 flame, but the peak value of OH* radiation is higher.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
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